What we know and don't know about Asiana Flight 214

By Richard T. Griffiths, CNN

Updated 2129 GMT (0529 HKT) July 8, 2013

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Photos:Plane crash-lands in San Francisco

Plane crash-lands in San Francisco – In this handout photo released by the National Transportation Safety Board, Asiana Airlines Flight 214 sits just off the runway at San Francisco International Airport on Sunday, July 7. The Boeing 777 coming from Seoul, South Korea, crashed on landing on Saturday, July 6. Three passengers, all girls, died as a result of the first notable U.S. air crash in four years.

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Photos:Plane crash-lands in San Francisco

Plane crash-lands in San Francisco – A photo showing the damaged interior of the aircraft was released by the NTSB on July 7. The flight carrying 291 passengers and 16 crew took off from Shanghai and stopped in Seoul before heading to San Francisco.

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Photos:Plane crash-lands in San Francisco

Plane crash-lands in San Francisco – An investigator photographs part of the landing gear at the crash site in a handout released on July 7. Investigators believe that the pilots were flying too slow and too low as they neared the airport on July 6.

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Photos:Plane crash-lands in San Francisco

Plane crash-lands in San Francisco – An investigator inspects the broken-off tail of the plane in a handout photo released July 7. The crash killed two people, injured 182 and forced the temporary closure of one of the country's largest airports.

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Photos:Plane crash-lands in San Francisco

Plane crash-lands in San Francisco – An investigator stands near the tail of the plane in a handout photo released on July 7. The NTSB has ruled out weather as a problem and said that conditions were right for a "visual landing."

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Photos:Plane crash-lands in San Francisco

Plane crash-lands in San Francisco – Investigators approach the crash in a handout photo released on July 7.

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Plane crash-lands in San Francisco – Fire crews attempt to quench the blaze on Saturday, July 6.

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Plane crash-lands in San Francisco – Smoke rises from the crash site across the San Francisco Bay on July 6.

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Plane crash-lands in San Francisco – Asiana Airlines Flight 214 remains on the runway on July 6.

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Plane crash-lands in San Francisco – A plane sits on the runway on July 6 while emergency crews tend to the crash site.

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Photos:Plane crash-lands in San Francisco

Plane crash-lands in San Francisco – A helicopter flies above the wreckage on July 6 as people observe from across the waters of San Francisco Bay.

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Plane crash-lands in San Francisco – Travelers at San Francisco International Airport look at the departures and arrivals board after Asiana Flight 214 crashed on July 6. The airport, located 12 miles south of downtown San Francisco, is California's second busiest, behind Los Angeles International.

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Photos:Plane crash-lands in San Francisco

Plane crash-lands in San Francisco – Kevin Cheng talks on his phone as he waits in the terminal after Asiana Airlines Flight 214 crash-landed on July 6. He said he was supposed to pick up students who were on board the flight from Seoul.

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Photos:Plane crash-lands in San Francisco

Plane crash-lands in San Francisco – Passengers wait for the British Airways counter to reopen at San Francisco International Airport on July 6.

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Plane crash-lands in San Francisco – Police guard the Reflection Room at the San Francisco airport's international terminal, where passengers from Asiana Airlines Flight 214 were reportedly gathering after the crash landing on July 6.

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Photos:Plane crash-lands in San Francisco

Plane crash-lands in San Francisco – People are escorted from the Reflection Room at the San Francisco International Airport on July 6.

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Plane crash-lands in San Francisco – Traffic backs up on U.S. Route 101 South in San Francisco on July 6. The Bay Area airport was closed to incoming and departing traffic after the crash, according to the Federal Aviation Administration.

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Plane crash-lands in San Francisco – People look over the wreckage across a cove in San Francisco Bay on July 6.

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Plane crash-lands in San Francisco – Deborah Hersman, chairwoman of the National Transportation Safety Board, speaks to the press at Reagan National Airport in Arlington, Virginia, before departing for San Francisco with an NTSB crew on July 6 to investigate the crash site.

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Photos:Plane crash-lands in San Francisco

Plane crash-lands in San Francisco – The San Francisco Giants observe a moment of silence for those killed and hurt in the crash before their baseball game on July 6 against the Los Angeles Dodgers at AT&T Park in San Francisco.

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Plane crash-lands in San Francisco – Crews comb the end of a San Francisco airport runway following the crash landing on July 6.

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Plane crash-lands in San Francisco – People in Seoul watch a news program reporting about the crash landing on July 6 in San Francisco. Asiana Airlines Flight 214 took off from Seoul earlier Saturday.

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Plane crash-lands in San Francisco – The plane crashed on July 6 around 11:30 a.m. (2:30 p.m. ET).

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Plane crash-lands in San Francisco – People walk past the wreckage of the plane's tail on July 6.

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Plane crash-lands in San Francisco – The burned-out plane remains on the runway on July 6. Passengers and crew members escaped down the emergency inflatable slides.

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Plane crash-lands in San Francisco – Rescue workers tend to the crash site on July 6.

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Plane crash-lands in San Francisco – Debris litters the runway on July 6.

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Plane crash-lands in San Francisco – Airport shuttles arrive on the scene after the crash landing.

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Plane crash-lands in San Francisco – Wreckage from the Boeing 777 lies on the tarmac on July 6.

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Plane crash-lands in San Francisco – Crews surround the remains of the plane on July 6.

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Plane crash-lands in San Francisco – Investigators pass the detached tail and landing gear of Asiana Airlines Flight 214 on July 6.

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Plane crash-lands in San Francisco – An aerial view shows the site of the crash landing between the runways on July 6.

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Plane crash-lands in San Francisco – Smoke rises from the crash site on July 6 at the airport in San Francisco.

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Plane crash-lands in San Francisco – Fire crews work at the crash site at San Francisco International Airport on July 6.

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Plane crash-lands in San Francisco – The Boeing 777 lies burned on the runway after it crashed landed on July 6.

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Plane crash-lands in San Francisco – An aerial photo of the scene on July 6 shows the extent of the plane's damage.

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Plane crash-lands in San Francisco – The burned-out plane sits surrounded by emergency vehicles on July 6.

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Plane crash-lands in San Francisco – CNN iReporter Amanda Painter took this photo while waiting at the San Francisco airport on July 6. The entire airport has shut down and flights diverted to other airports.

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Photos:Plane crash-lands in San Francisco

Plane crash-lands in San Francisco – iReporter Val Vaden captured this photo while waiting in a departure lounge at the San Francisco airport on July 6. Val observed the billowing smoke and emergency responders' rush in.

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Plane crash-lands in San Francisco – iReporter Sven Duenwald was at home on July 6 when he saw smoke rising into the air near the San Francisco International Airport.

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Photos:Plane crash-lands in San Francisco

Plane crash-lands in San Francisco – iReporter Timothy Clark was standing on the eighth floor of the Embassy Suites Airport Hotel when he heard a loud crashing sound from outside. "My daughter told me she heard a plane crash. I used my camera to get a clearer view and I could see a dust cloud. Then people running from the plane, then flames," he said.

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Photos:Plane crash-lands in San Francisco

Plane crash-lands in San Francisco – A photo provided to CNN by Eunice Bird Rah -- and shot by her father, who was a passenger on the plane -- shows flames and smoke bursting out of many of the aircraft's windows.

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Photos:Plane crash-lands in San Francisco

Plane crash-lands in San Francisco – David Eun, a passenger on Asiana Airlines Flight 214, posted this image to Path.com along with the message, "I just crash landed at SFO. Tail ripped off. Most everyone seems fine, I'm ok. Surreal..." It was one of the first photographs taken after the crash.

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Story highlights

Airline: Pilot was making first landing in control of a Boeing 777 at San Francisco airport

Pilot had 10,000 hours of experience but only 43 hours flying time in a 777

An emergency vehicle ran over one of the passengers

Passengers describe the engines spooling up and the nose tilting up before impact

1. A preliminary readout from the flight data and cockpit voice recorders shows the aircraft was approaching well below the target landing speed of 137 knots (157 mph). Records from the flight data recorder show that at 500 feet of altitude and 34 seconds before impact, the aircraft had already slowed to 134 knots (154 mph).

At seven seconds before impact, the pilots attempted to spool up the engines. At four seconds, the stall warning sounded. At 1.5 seconds, the pilots tried to abort the landing and go around to attempt another landing. At impact, the flight data recorder shows the aircraft had a forward speed of a mere 106 knots (121 mph).

What we don't know: Why was the aircraft approaching so slowly? Did the pilot not realize he was short?

2. Asiana said the pilot at the controls was making his first landing of a Boeing 777 at San Francisco International Airport. While a pilot with more than 10,000 hours of experience, including many hours flying Boeing 747s, he had only 43 hours of flying time in a 777.

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What we don't know: Did pilot inexperience with the aircraft play a role? Why did the captain not speak up or take control?

3. The NTSB investigators have found nothing to corroborate online flight tracking records showing that Asiana Flight 214 descended from cruising altitude much more steeply and rapidly than previous Asiana flights on the same route. The NTSB says it found no "abnormally steep descent data."

4. Part of the instrument landing system approach on Runway 28L was not working on the day of the crash. It had been down for some time. Flights were landing using visual flight rules. The weather was clear. The flight data shows the autopilot was disengaged at 1,600 feet and the pilot then took manual control of the plane.

What we don't know: Did the lack of ILS force the pilot to make a VFR landing in an aircraft with which he was not fully familiar?

What we don't know: Why didn't the pilot recognize he was too low for the approach and initiate a go-around earlier?

6. Based on the debris field and the video obtained by CNN, the aircraft appears to have struck the rock sea wall well before the start of the runway. There are some marks on the sea wall, consistent with an impact of some part of the plane.

7. The debris field runs from the water, slightly right of the paved threshold and runway center, all the way to the stopped aircraft fuselage. The NTSB says pieces of the rear of the aircraft are in the water near the seawall, visible at low tide.

8. The Boeing 777 lost its tail section, including vertical and horizontal stabilizers, near the end of the paved threshold, just before the start of the runway.

What we don't know: Is this an indication the tail of the aircraft detached after first impact?

9. The right engine is detached from the wing and wedged against the right side of the fuselage. The left engine is a considerable distance forward of the fuselage in a grassy area to the right of Runway 28L. The NTSB says both engines had high rotational damage, showing that they were powering at impact.

10. Most of the fire damage to the aircraft occurred after the Boeing 777 came to a stop on its belly.

11. Passengers described the cabin interior as heavily damaged, with overhead bins dropping and at least one life raft/escape slide inflating inside the aircraft, trapping a flight attendant, whom passengers helped free. The NTSB says it will investigate the structural safety of the seats.

12. The coroner says one of the two passengers killed appears to have been run over by an emergency vehicle, though the coroner had not yet determined the cause of death. Asiana has identified the fatalities as Ye Mengyuan and Wang Linjia of China, both of whom were 16.

13. Audio recordings of air traffic control conversations show no sign that the pilot declared an emergency before the crash landing. Emergency vehicles were dispatched afterward.

14. The aircraft was built in 2006 and was purchased new by Asiana.

15. The NTSB was planning to interview the four pilots Monday afternoon. Key information from those interviews will be made public at Tuesday's briefing.